1. Field of the Invention
The present invention relates to an optical pick-up head and an information recording/reproducing apparatus.
2. Description of the Related Art
An optical memory technique using an optical disk with a pit pattern as a high-density and large-capacity storage medium has been put into practical use. Such an optical memory technique is utilized for a digital audio disk, a video disk, and a data file disk. A digital versatile disc (DVD) that is becoming widespread in recent years is a high-density optical disk using a semiconductor laser with a wavelength of 650 nm as a light source. Regarding DVDs, various media such as a DVD-ROM dedicated to reproduction, a write-once, read-many-times DVD-R, and a DVD-RAM that is recordable many times have been standardized.
Conventionally, various optical pick-up heads have been reported, which record and/or reproduce information with respect to the above-mentioned optical disks. As an example of a conventional optical pick-up head, the structure of an integrated optical pick-up head 100 disclosed in JP 2675977 is shown schematically in FIG. 8 (hatching is omitted).
Referring to FIG. 8, the optical pick-up head 100 includes a semiconductor substrate 101 and a laser diode 102. A photodiode 103 is formed on the semiconductor substrate 101.
The semiconductor substrate 101 is an n-type and has a concave portion. The laser diode 102 is a single-mode oscillation laser. The laser diode 102 is mounted in the concave portion of the semiconductor substrate 101 via an insulating layer 104. The photodiode 103 is formed on a side surface of the concave portion, and outputs a current depending upon the laser output from the laser diode 102. The current from the photodiode 103 is converted into a voltage signal by a resistor 105, and the voltage signal is output from a terminal 106. The voltage signal is input to a power control circuit from the terminal 106. The power control circuit controls the operating current flowing through the laser diode 102 so that the laser output from the laser diode 102 has a desired value. A voltage of +5 volts is applied to the semiconductor substrate 101 from a terminal 107 so as to supply a reverse bias voltage to the photodiode 103. The surface of the laser diode 102 that is in contact with the insulating layer 104 is connected to a terminal 108, and the opposite surface thereof is connected to a terminal 109. A high-frequency signal of hundreds of MHz is supplied from an npn transistor 110 to the terminal 109 so as to modulate the output from the laser diode 102. In the optical pick-up head 100, the output from the laser diode 102 is modulated, whereby the output from the laser diode 102 is prevented from fluctuating due to a laser beam that is reflected from an optical storage medium and is incident upon the laser diode 102.
The optical pick-up head 100 includes a photodetector for detecting a laser beam reflected from the optical storage medium. The optical pick-up head is miniaturized and produced easily by forming such a photodetector on the semiconductor substrate 101.
However, in the case of forming the photodetector on the semiconductor substrate 101, the photodetector is influenced by a high-frequency signal to cause an offset in a focus error signal and a tracking error signal. This is because a high-frequency signal applied to the laser diode 102 also is applied to the semiconductor substrate 101 via the insulating layer 104.
Therefore, with the foregoing in mind, it is an object of the present invention to provide an optical pick-up head applying a high-frequency signal to a semiconductor laser in which an offset is unlikely to occur in a focus error signal and a tracking error signal, and an information recording/reproducing apparatus using the optical pick-up head.
In order to achieve the above-mentioned object, the optical pick-up head of the present invention includes a semiconductor substrate; a semiconductor laser mounted on the semiconductor substrate; a photodetector for receiving a laser beam emitted from the semiconductor laser and reflected from an optical storage medium and outputting a current signal in accordance with a light amount of the received laser beam; and a current-voltage conversion circuit for converting the current signal into a voltage signal, wherein the semiconductor laser is supplied with a high-frequency signal for preventing an output from fluctuating due to the laser beam reflected from the optical storage medium, and the photodetector and the current-voltage conversion circuit are formed on the semiconductor substrate. According to this construction, the photodetector for receiving a laser beam reflected from the optical storage medium is formed on the semiconductor substrate on which the semiconductor laser is mounted. Therefore, an optical pick-up head is obtained in which characteristics are unlikely to be changed over time. Furthermore, in the above-mentioned optical pick-up head, a high frequency is applied to the semiconductor laser, so that an output of the semiconductor laser is stable. Furthermore, in the above-mentioned optical pick-up head, the photodetector and the current-voltage conversion circuit are formed on the semiconductor substrate on which the semiconductor laser is mounted. Therefore, the optical pick-up head is less influenced by a high-frequency signal input to the semiconductor laser. Therefore, an optical pick-up head is obtained in which an offset is unlikely to occur in a focus error signal and a tracking error signal.
In the above-mentioned optical pick-up head, the semiconductor substrate may be of a p-type. According to this construction, the semiconductor substrate can be grounded, so that the electric potential of the semiconductor substrate is stabilized, and the influence of a high-frequency signal in particular can be minimized.
In the above-mentioned optical pick-up head, the semiconductor laser may include a substrate and an active layer formed above the substrate, and the semiconductor laser may be mounted on the semiconductor substrate so that the active layer is closer to the semiconductor substrate than the substrate. According to this construction, heat generated by the semiconductor laser rapidly is transferred to the semiconductor substrate, so that an optical pick-up head with particularly high reliability can be obtained.
In the above-mentioned optical pick-up head, a frequency f1, at which a gain of the current-voltage conversion circuit becomes xe2x88x923 dB, and a frequency f2 of the high-frequency signal may satisfy a relationship f2/f1xe2x89xa65. According to this construction, an optical pick-up head is obtained that allows information to be reproduced rapidly and has less unwanted emission.
Furthermore, the information recording/reproducing apparatus of the present invention for at least reproducing information from an optical storage medium includes: the above-mentioned optical pick-up head of the present invention; a driving unit for changing a relative position between the optical storage medium and the optical pick-up head; and a signal processing circuit for obtaining information recorded on the optical storage medium by using a signal output from the optical pick-up head. In the above-mentioned information recording/reproducing apparatus, the optical pick-up head of the present invention is used, so that an offset does not occur in a signal output from the current-voltage conversion circuit. As a result, a highly reliable information recording/reproducing apparatus can be realized.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.